The subject matter of the present invention relates generally to wood veneer peeling and in particular to a veneer lathe apparatus having a plurality of powered drive rolls which contact the side of a log to clamp such log between such rolls for rotating the log about a lathe axis during peeling. Three powered drive rolls are preferably employed so that the lathe spindles which contact the opposite ends of the log for rotation thereof can be eliminated or reduced in size thereby enabling the log to be peeled to a smaller diameter of about 31/2 inches or less. Lathe spindles may be employed to rotate the log during initial peeling until the diameter of the log is reduced to a predetermined diameter at which time the powered drive rolls are moved into engagement with the sides of the log to supply additional torque for rotating the log or for supplying all of the torque for rotation if the lathe spindles are disengaged.
The three drive rolls extend over the major portion of the length of the log to prevent deflection of the log when it is peeled to a small diameter which would otherwise cause thickness variations in the veneer. One of the drive rolls is locked in a reference position during peeling and serves as a reference roll for the other two drive rolls in clamping the log with its optimum yield axis in alignment with the lathe axis. U.S. Pat. No. 4,197,888 of McGee et al. issued Apr. 15, 1980 shows how the optimum yield axis of a log can be determined automatically by scanning it with light beams. The position of the reference roll is adjusted automatically toward the lathe axis and arcuately about such axis in response to movement of the lathe knife during peeling to maintain the reference roll in contact with the log and to keep the log aligned with the lathe axis.
It has been previously proposed in U.S. Pat. No. 4,073,326 of Pank et al issued Feb. 14, 1978 to provide a veneer peeling machine employing two powered drive rolls called pressure rolls and one idler roll called a reaction roll for clamping the log between such rolls and thereby eliminating the need for lathe spindles engaging the opposite ends of the log. However, unlike the present invention, the idler roll is not a powered roll and, while being a reaction roll against which the log is urged by the two powered pressure rolls, such idler roll does not serve as an independent reference for the other two powered drive rollers. Thus, the movement of the reaction roll of such apparatus is guided by a cam mounted on the support of one of the pressure rolls and is not locked in a vertical reference position on a cam separate from the other drive rolls which is adjusted in accordance with the position of the lathe knife, in the manner of the present invention. The two pressure rolls are not mounted on a common support so that the spacing between such rolls is fixed, but the spacing is changed during peeling to move the pressure rolls toward a reference plane. In addition, this patent does not disclose the use of an eccentric to change the pivot points of the support arms for the two powered pressure rolls in order to maintain such rolls in contact with the log, in the manner of the present invention.
U.S. Pat. No. 2,884,966 of Zilm issued May 5, 1959, also shows a veneer lathe having two powered drive rolls. His two powered rolls are coupled together and mounted on a common support so that the spacing between such rolls is fixed. However, these drive rolls only extend over a short portion of the length of the log which is much less than the major portion of such length, and therefore, cause deflection in the form of a compound bowing of the log when it is peeled to a small diameter. This deflection produces non-uniformities in the thickness of the veneer width across the veneer strip. Also, this lathe does not use a third powered drive roll.
U.S. Pat. No. 3,421,560 of Springate issued Jan. 14, 1969 shows a similar teaching, except that he employs two longitudinally spaced pairs of idler back-up rolls, each pair mounted on a common support which pivot into contact with the log by a cam means. Unlike the present invention, there is no reference drive roll which is locked in a vertical reference position and against which the log is urged by two other drive rolls. However, such patent discloses a lathe knife means having a nose bar with a powered roller which is driven by contact with another roller in the nose bar assembly. Springate also suffers from the defect that his back-up rolls do not contact the log over a major portion of its length and therefore permit deflection which would apparently be in the form of double compound bowing of the log when its diameter is reduced to a small diameter.
It has previously been proposed in the veneer lathe apparatus of U.S. patent application Ser. No. 224,081 of Brookhyser et al filed Jan. 12, 1981 to employ a powered back-up roll and an idler roll which extend along the major portion of the length of the log to prevent deflection of a log core of small diameter. However, this prior lathe apparatus does not employ a plurality of powered drive rolls to clamp the log between such rolls so that the latch spindles can be eliminated and does not include a cam for locking a reference drive roll in a reference position so that it serves as a reference surface for the other two drive rolls, in the manner of the present invention.
The veneer lathe apparatus of the present invention has several advantages over the previous lathe apparatus including the ability to apply more torque or rotational force to the log by employing three powered drive rolls which clamp the log between such rolls. The use of three powered drive rolls provides sufficient torque power so that lathe spindles or chucks which normally engage the opposite ends of the log can be eliminated or replaced with smaller spindles, thereby enabling the log to be peeled to a smaller diameter. In addition, by eliminating the need for such lathe spindles or reducing the torque which must be applied to such spindles at small log diameters, breakage of the ends of the log and/or spin-out of the lathe spindles from such ends is prevented. Furthermore, since the three powered drive rolls extend along the major portion of the length of the log, deflection of the log is prevented when it is peeled to a small diameter so that the veneer thickness is more uniform across the width of the veneer strip.
By employing one of the three powered drive rolls as a reference roll for the other two rolls and locking such reference roll in a vertical reference position that is adjusted relative to the lathe axis automatically in response to reductions in the log diameter by sensing the position of the lathe knife, more accurate peeling of veneer with a predetermined thickness is achieved. The veneer lathe drive of the present invention is simple, reliable and accurate in operation because it uses a cam means for determining the reference position of the reference roll independent of the other two drive rolls and employs an eccentric to change the pivot point of the common support arm for the two other drive rolls in order to maintain such other rolls in contact with the log at all times during peeling in spite in reductions in diameter of the log. Another advantage of the present lathe roll drive is that a more efficient drive coupling between the drive rolls and the log is achieved without reducing accuracy in the veneer peeling by providing the surface of the reference roll of a rigid material such as metal while providing the surface of the other two drive rolls with a compressible high friction material such as polyurethane or other elastomer material.